Display apparatus and electronic device

ABSTRACT

[Object] To provide a display apparatus that can achieve enhancement in display performance of a screen and higher definition. 
     [Solution] There is provided a display apparatus. The drive circuit includes a drive transistor configured to control the light emitting unit, a video signal writing transistor configured to control writing of a video signal, and a capacitative element. In the drive transistor, one source/drain region is connected to a current supply line, another source/drain region is connected to the light emitting unit and a first node of the capacitative element, and a gate electrode is connected to a second node of the capacitative element. In the video signal writing transistor, one source/drain region is connected to a data line, another source/drain region is connected to the gate electrode of the drive transistor and the second node of the capacitative element, and a gate electrode is connected to a scanning line. The drive transistor and the video signal writing transistor are different in carrier mobility.

CROSS REFERENCES TO RELATED APPLICATIONS

The present Application is a Continuation Application of U.S. patentapplication Ser. No. 17/380,346 filed Jul. 20, 2021, which is aContinuation Application of U.S. patent application Ser. No. 16/088,162filed Sep. 25, 2018, now U.S. Pat. No. 11,081,057 issued Aug. 3, 2021,which is a 371 National Stage Entry of International Application No.:PCT/JP2017/009691, filed on Mar. 10, 2017, which in turn claims priorityfrom Japanese Application No. 2016-085682, filed on Apr. 22, 2016, theentire contents of which are incorporated herein by reference.

TECHNICAL FIELD The present disclosure related to a display apparatusand an electronic device. BACKGROUND ART

In recent years, an organic electroluminescence display apparatus(hereinafter, sometimes simply abbreviated to as an “organic EL displayapparatus”) that uses an organic electroluminescence device(hereinafter, sometimes simply abbreviated to as an “organic EL device”)attracts attention. The organic EL display apparatus is of aself-light-emitting type, and has a characteristic of low powerconsumption, and moreover, has sufficient responsivity even to ahigh-definition high-speed video signal. Thus, the development forpractical application and product commercialization of the organic ELdisplay apparatus are earnestly promoted (e.g. refer to PatentLiteratures 1 and 2, etc.).

CITATION LIST Patent Literature

Patent Literature 1: JP 2013-44890A

Patent Literature 2: JP 2012-255874A

DISCLOSURE OF INVENTION Technical Problem

Higher definition of the organic EL display apparatus can be achieved bypromoting the miniaturization of a drive circuit. Therefore, inpromoting the miniaturization of a drive circuit, it is desired tominiaturize the drive circuit without deteriorating display performanceof a screen.

In view of the foregoing, the present disclosure proposes a displayapparatus and an electronic device that are novel and improved, and canachieve enhancement in display performance of a screen and higherdefinition.

Solution to Problem

According to the present disclosure, there is provided a displayapparatus including: a plurality of light emitting devices eachincluding a light emitting unit and a drive circuit for driving thelight emitting unit. The drive circuit includes a drive transistorconfigured to control the light emitting unit, a video signal writingtransistor configured to control writing of a video signal, and acapacitative element. In the drive transistor, one source/drain regionis connected to a current supply line, another source/drain region isconnected to the light emitting unit and a first node of thecapacitative element, and a gate electrode is connected to a second nodeof the capacitative element. In the video signal writing transistor, onesource/drain region is connected to a data line, another source/drainregion is connected to the gate electrode of the drive transistor, and agate electrode is connected to a scanning line. The drive transistor andthe video signal writing transistor are different in carrier mobility.

In addition, according to the present disclosure, there is provided anelectronic device including: the display apparatus.

Advantageous Effects of Invention

As described above, according to the present disclosure, a displayapparatus and an electronic device that are novel and improved, and canachieve enhancement in display performance of a screen and higherdefinition can be provided.

Note that the effects described above are not necessarily limitative.With or in the place of the above effects, there may be achieved any oneof the effects described in this specification or other effects that maybe grasped from this specification.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an explanatory diagram illustrating cross-sectional examplesof a drive transistor and a video signal writing transistor.

FIG. 2 is an explanatory diagram illustrating a configuration example ofan organic EL display apparatus according to an embodiment of thepresent disclosure.

FIG. 3 is an explanatory diagram illustrating a configuration example ofeach pixel 15 of a pixel array portion 11.

FIG. 4 is an explanatory diagram illustrating an operation example ofthe pixel 15 as a timing chart.

FIG. 5 is an explanatory diagram illustrating a configuration example ofcross sections of a video signal writing transistor Tsig and a drivetransistor Tdrv that are formed in the pixel 15.

FIG. 6 is an explanatory diagram illustrating another configurationexample of cross sections of the video signal writing transistor Tsigand the drive transistor Tdrv that are formed in the pixel 15.

FIG. 7 is an explanatory diagram illustrating a cross-sectional exampleof the pixel 15.

FIG. 8 is an explanatory diagram illustrating a cross-sectional exampleof the pixel 15.

FIG. 9 is an explanatory diagram illustrating an example of a voltagecurrent characteristic of the drive transistor Tdrv.

FIG. 10 is an explanatory diagram illustrating another cross-sectionalexample of the pixel 15.

MODE(s) FOR CARRYING OUT THE INVENTION

Hereinafter, (a) preferred embodiment(s) of the present disclosure willbe described in detail with reference to the appended drawings. Notethat, in this specification and the appended drawings, structuralelements that have substantially the same function and structure aredenoted with the same reference numerals, and repeated explanation ofthese structural elements is omitted.

Note that the description will be given in the following order.

-   -   1. Embodiment of Present Disclosure        -   1.1. Overview        -   1.2. Configuration Examples of Display Apparatus and Pixel        -   1.3. Operation Example of Pixel        -   1.4. Cross-Sectional Example    -   2. Conclusion

1. Embodiment of Present Disclosure 1.1. Overview

First of all, before an embodiment of the present disclosure isdescribed in detail, an overview of an embodiment of the presentdisclosure will be described.

As described above, in recent years, an organic electroluminescencedisplay apparatus (hereinafter, sometimes simply abbreviated to as an“organic EL display apparatus”) that uses an organic EL device attractsattention. The organic EL display apparatus is of a self-light-emittingtype, and has a characteristic of low power consumption, and moreover,has sufficient responsivity even to a high-definition high-speed videosignal. Thus, the development for practical application and productcommercialization of the organic EL display apparatus are earnestlypromoted.

As one of drive circuits that drive pixels of the organic EL displayapparatus, there is a 2Tr drive circuit including, for one pixel, twotransistors including a drive transistor for driving an organic ELdevice, and a video signal writing transistor for writing a videosignal.

When a drive circuit of the organic EL display apparatus is formed on asilicon wafer by a silicon semiconductor process, the miniaturizationbecomes easier. When the drive circuit can be miniaturized, higherdefinition of the organic EL display apparatus can be achieved. On theother hand, in a case where an n-channel type metal-oxide semiconductor(MOS) transistor is used as the drive transistor, and a p-type well isinstalled for stabilization of an operation of the drive transistor,when the organic EL device emits light, a source electric potential ofthe drive transistor also rises. When the source electric potential ofthe drive transistor rises, electric potentials of the p-type well andthe drive transistor also rise. When the electric potentials of thep-type well and the drive transistor also rise, current of the drivetransistor decreases due to a so-called substrate bias effect. When thecurrent of the drive transistor decreases, luminance of the organic ELdevice declines.

In view of the foregoing, Patent Literature 1 described above disclosesa technology of forming a drive transistor in a p-type well in a buriedn-type well formed in a p-type silicon substrate, and electricallyconnecting a source of the drive transistor and the p-type well, forsuppressing the substrate bias effect. In this technology, thesuppression of the substrate bias effect becomes possible, whereas it isnecessary to electrically separate p-type wells of drive transistorsbetween adjacent drive circuits.

FIG. 1 is an explanatory diagram illustrating cross-sectional examplesof a drive transistor and a video signal writing transistor. FIG. 1illustrates an example in which a drive transistor is formed in a p-typewell in a buried n-type well formed in a p-type silicon substrate. Asillustrated in FIG. 1 , when the n-type well is formed between p-typewells of drive transistors for electrically separating the p-type wellsof the drive transistors between adjacent drive circuits, theminiaturization of the drive circuits becomes difficult.

When a drive circuit is to be miniaturized, it is necessary to reducethe size of a drive transistor for securing a space in which an n-typewell region is to be formed. Nevertheless, for example, when a gatelength is reduced, a characteristic variation of drive transistorsincreases. An increase in a characteristic variation of drivetransistors leads to an increase in a luminance variation of organic ELdevices provided in the respective drive circuits, and the uniformity ofa screen is impaired. Accordingly, when a drive transistor is formed ina p-type well in a buried n-type well formed in a p-type siliconsubstrate, it becomes difficult to achieve both of the miniaturizationof the drive circuit, and enhancement in the uniformity of the screen.

In addition, there is a technology of using a MOS transistor formed on amonocrystal silicon wafer, as a drive transistor. Nevertheless, when aMOS transistor formed on a monocrystal silicon wafer is used as a drivetransistor, mobility correction is excessively applied, and theuniformity of the screen is impaired. Patent Literature 2 discloses atechnology of suppressing display unevenness caused by a phenomenon inwhich mobility correction is excessively applied. Patent Literature 2discloses a technology of avoiding excessive application of mobilitycorrection by controlling an electric potential of a p-type well (backgate) of a drive transistor such that threshold voltage gets higher.Nevertheless, when a circuit or a terminal that controls substrate biasis provided, higher integration of the drive circuit, that is to say,higher definition of a display apparatus is prevented.

Thus, in view of the above-described content, the disclosing party ofthe present application earnestly studied a technology that can achieveenhancement in display performance of a screen and higher definition, ina display apparatus that uses a self-light emitting device such as anorganic EL device. As a result, the disclosing party of the presentapplication has eventually devised a technology that can achieveenhancement in display performance of a screen and higher definition, ina display apparatus that uses a self-light emitting device, as describedbelow.

The overview of the embodiment of the present disclosure has beendescribed above.

1.2. Configuration Examples of Display Apparatus and Pixel

Subsequently, a configuration example of an organic EL display apparatusaccording to an embodiment of the present disclosure will be described.FIG. 2 is an explanatory diagram illustrating a configuration example ofan organic EL display apparatus according to an embodiment of thepresent disclosure. A configuration example of an organic EL displayapparatus according to an embodiment of the present disclosure will bedescribed below using FIG. 2 .

Note that, in the following description of a circuit configuration,“electrical connection” will be simply described as “ connection”, andthe “electrical connection” is not limited to direct connection, andincludes connection established via another transistor (switchingtransistor is a typical example), or another electrical element (notlimited to an active element, and may be a passive element).

As illustrated in FIG. 2 , an organic EL display apparatus 1 accordingto the embodiment of the present disclosure includes a pixel arrayportion 11, a light scanner 12, a drive scanner 13, and a horizontalselector 14.

In the pixel array portion 11, a plurality of pixels 15 each includingan organic EL device OLED are two-dimensionally arrayed in a matrix. Ina case where the organic EL display apparatus 1 supports color display,one pixel (unit pixel) serving as a unit of forming a color imageincludes a plurality of subpixels, and each of the subpixels correspondsto the pixel 15 in FIG. 2 . Specifically, in a display apparatussupporting color display, one pixel includes three subpixels including asubpixel that emits red (R) light, a subpixel that emits green (G)light, and a subpixel that emits blue (B) light, for example. Note thatone pixel is not limited to a combination of subpixels of RGB threecolors, and one pixel can further include a subpixel of another onecolor or subpixels of a plurality of colors in addition to the subpixelsof three colors. Specifically, one pixel can additionally include asubpixel that emits white (W) light for luminance enhancement, or onepixel can additionally include at least one subpixel that emitscomplementary color light for expanding a color reproduction range.

In the pixel array portion 11, with respect to an array of the pixels 15in m rows and n columns, a scanning line WS and a power supply line DSare laid for each pixel row along a row direction (an array direction ofpixels in a pixel row). Furthermore, with respect to the array of thepixels 15 in the m rows and the n columns, a signal line 16 is laid foreach pixel column along a column direction (an array direction of pixelsin a pixel column).

Each of the scanning lines WS is connected to the end of a correspondingrow of the light scanner 12. Each of the power supply lines DS isconnected to the end of a corresponding row of the drive scanner 13.

The light scanner 12 includes a shift register circuit that sequentiallyshifts (transfers) start pulses in synchronization with clock pulses,and the like. The light scanner 12 sequentially scans (performs linesequential scanning of) the pixels 15 of the pixel array portion 11 on arow basis by sequentially supplying writing scanning signals to thescanning lines WS, in writing signal voltage of a video signal into eachof the pixels 15 of the pixel array portion 11.

The drive scanner 13 includes a shift register circuit that sequentiallyshifts start pulses in synchronization with clock pulses, and the like.In synchronization with the line sequential scanning performed by thelight scanner 12, the drive scanner 13 supplies, to the power supplylines DS, a power source electric potential switchable between a firstpower source electric potential Vccp and a second power source electricpotential Vini that is lower than the first power source electricpotential Vccp. By the switching of the power source electric potentialbetween the first power source electric potential Vccp and the secondpower source electric potential Vini, the control of a light-emittingstate and a non-light-emitting state of each of the pixels 15 isperformed.

The horizontal selector 14 selectively outputs signal voltage Vsig of avideo signal corresponding to luminance information that is suppliedfrom a signal supply source (not illustrated), and reference voltageVofs. Here, the reference voltage Vofs is an electric potential servingas a reference of the signal voltage Vsig of the video signal (e.g.electric potential corresponding to a black level of the video signal),and is used in threshold value correction processing to be describedlater.

The signal voltage Vsig and the reference voltage Vofs that are outputfrom the horizontal selector 14 are written into each of the pixels 15of the pixel array portion 11 via the signal line 16, in a unit of apixel row selected by the scanning performed by the light scanner 12. Inother words, the horizontal selector 14 employs a driving mode of linesequential writing that writes the signal voltage Vsig on a row basis.

The configuration example of the organic EL display apparatus 1according to the embodiment of the present disclosure has been describedabove using FIG. 2 . Subsequently, a specific configuration example ofeach of the pixels 15 of the pixel array portion 11 will be described.

FIG. 3 is an explanatory diagram illustrating a configuration example ofeach of the pixels 15 of the pixel array portion 11 in the organic ELdisplay apparatus 1 according to the embodiment of the presentdisclosure. A configuration example of the pixel 15 will be describedbelow using FIG. 3 .

As illustrated in FIG. 3 , the pixel 15 includes the organic EL deviceOLED, a drive transistor Tdrv, a video signal writing transistor Tsig, ahold capacitance Cs, and an auxiliary capacitance Cel.

In the organic EL device OLED, a cathode electrode is connected to thepower supply line DS laid for all the pixels 15 in common. In addition,a drive circuit for driving the organic EL device OLED includes thedrive transistor Tdrv, the video signal writing transistor Tsig, thehold capacitance Cs, and the auxiliary capacitance Cel.

In the drive transistor Tdrv, one electrode (source/drain electrode) isconnected to an anode electrode of the organic EL device OLED, andanother electrode (source/drain electrode) is connected to the powersupply line DS. In addition, a back gate of the drive transistor Tdrv isgrounded.

In the video signal writing transistor Tsig, one electrode (source/drainelectrode) is connected to the signal line 16, and another electrode(source/drain electrode) is connected to a gate electrode of the drivetransistor Tdrv. In addition, a gate electrode of the video signalwriting transistor Tsig is connected to the scanning line WS.

In the drive transistor Tdrv and the video signal writing transistorTsig, one electrode refers to a metal line electrically connected to asource/drain region, and another electrode refers to a metal lineelectrically connected to a drain/source region. In addition, dependingon an electric potential relationship between one electrode and anotherelectrode, the one electrode can serve as a source electrode or a drainelectrode, and the other electrode can serve as a drain electrode or asource electrode.

In the present embodiment, transistors different in carrier mobility areused as the drive transistor Tdrv and the video signal writingtransistor Tsig. For example, a MOS transistor formed on a silicon (Si)semiconductor substrate is used as the video signal writing transistorTsig, and a thin film transistor (TFT) is used as the drive transistorTdrv, and both transistors are separately used. In the presentembodiment, for example, an n-channel type MOSTFT is used as the videosignal writing transistor Tsig. Note that a conductivity type of thevideo signal writing transistor Tsig may be a p-channel type.

The MOS transistor formed on the Si semiconductor substrate has such afeature that channel mobility is higher and a characteristic variationis smaller as compared with those in the case of using a polycrystallineor noncrystalline TFT. In the organic EL display apparatus 1 accordingto the present embodiment, by using the MOS transistor formed on the Sisemiconductor substrate, as the video signal writing transistor Tsig,owing to the feature described above, a video signal from a paneloutside can be input to a gate terminal of the drive transistor Tdrvwhile the quality thereof being maintained at high quality.

On the other hand, the TFT has a feature of being unaffected by asubstrate bias effect, because a body region is in an electricallyfloating state. Accordingly, in the organic EL display apparatus 1according to the present embodiment, by using the TFT as the drivetransistor, a decline in drive current that is caused by the substratebias effect, that is to say, deterioration in luminance as a displayapparatus can be suppressed. Furthermore, because the TFT has lowerchannel mobility as compared with that of a monocrystal Si-MOStransistor, in the pixel 15 illustrated in FIG. 3 , excessive mobilitycorrection as described above is not applied, and the uniformity of thescreen is not impaired, either. In the present embodiment, the drivetransistor Tdrv is formed so as to have lower carrier mobility thancarrier mobility of the video signal writing transistor Tsig. In thepixel 15 illustrated in FIG. 3 , by the drive transistor Tdrv beingformed so as to have lower carrier mobility than carrier mobility of thevideo signal writing transistor Tsig, the organic EL display apparatus 1according to the present embodiment can achieve enhancement in displayperformance of the screen.

In the hold capacitance Cs, one electrode (first node) is connected toanother source/drain region of the drive transistor Tdrv and the anodeelectrode of the organic EL device OLED, and another electrode (secondnode) is connected to the gate electrode of the drive transistor Tdrvand a source/drain region of the video signal writing transistor Tsig.

In the auxiliary capacitance Cel, one electrode is connected to theanode electrode of the organic EL device OLED, and another electrode isconnected to the power supply line DS. The auxiliary capacitance Cel isprovided for increasing a writing gain of a video signal with respect tothe hold capacitance Cs, for compensating for a capacitance shortageamount of an equivalent capacitance of the organic EL device OLED, byserving as an aid for the equivalent capacitance.

Note that FIG. 3 illustrates a configuration in which the otherelectrode of the auxiliary capacitance Cel is connected to the powersupply line DS, but a connect destination of the other electrode of theauxiliary capacitance Cel is not limited to the power supply line DS,and the connect destination is only required to be a node with a fixedelectric potential. By connecting the other electrode of the auxiliarycapacitance Cel to a node with a fixed electric potential, a capacitanceshortage amount of the organic EL device OLED can be compensated for,and a writing gain of a video signal with respect to the holdcapacitance Cs can be increased.

The specific configuration example of the pixel 15 has been describedabove using FIG. 3 . Subsequently, an operation example of the pixel 15of the organic EL display apparatus 1 will be described.

1.3. Operation Example of Pixel

FIG. 4 is an explanatory diagram illustrating an operation example ofthe pixel 15 of the organic EL display apparatus 1 according to theembodiment of the present disclosure, as a timing chart. An operationexample of the pixel 15 of the organic EL display apparatus 1 accordingto the embodiment of the present disclosure will be described belowusing FIG. 4 .

In the timing chart illustrated in FIG. 4 , respective changes of anelectric potential of the power supply line DS, an electric potential ofthe scanning line WS, an electric potential of the signal line 16(Vsig/Vofs), a gate electric potential Gate of the drive transistor Tdrvin the pixel 15 in FIG. 3 , and a source Source of the drive transistorTdrv are illustrated.

In FIG. 4 , a period before a time t0 is a light emitting period of theorganic EL device OLED in a previous display frame (previous frame). Inthe light emitting period of the previous frame, an electric potentialof the power supply line DS is at the first power source electricpotential (hereinafter, referred to as a high electric potential) Vccp,and in addition, the video signal writing transistor Tsig is in anonconductive state.

Here, the drive transistor Tdrv is designed so as to as to operate in asaturated region. Drive current (drain-source current) Ids correspondingto gate-source voltage Vgs of the drive transistor Tdrv is therebysupplied from the power supply line DS to the organic EL device OLEDthrough the drive transistor Tdrv. Then, the organic EL device OLEDemits light with luminance corresponding to a current value of the drivecurrent Ids.

At the time t0, the display frame shifts to a new display frame (currentframe) of line sequential scanning When threshold voltage of the drivetransistor Tdrv is denoted by Vth, the electric potential of the powersupply line DS switches from the high electric potential Vccp to thesecond power source electric potential (hereinafter, referred to as alow electric potential) Vini that is sufficiently lower than Vofs−Vthwith respect to the reference voltage Vofs of the signal line 16.

Here, threshold voltage of the organic EL device OLED is denoted byVthel, and an electric potential (a cathode electric potential) of acommon power supply line is denoted by Vcath. At this time, when the lowelectric potential Vini is set so as to satisfy Vini<Vthel+Vcath, anelectric potential of the Source becomes substantially equal to the lowelectric potential Vini. Thus, the organic EL device OLED enters areverse bias state, and goes out.

Subsequently, at a time t1, by the electric potential of the scanningline WS shifting from the low electric potential side to the highelectric potential side, the video signal writing transistor Tsig entersa conductive state. At this time, because the reference voltage Vofs isbeing supplied from the horizontal selector 14 to the signal line 16,the electric potential of the Gate becomes the reference voltage Vofs.In addition, the electric potential of the Source is at an electricpotential sufficiently lower than the reference voltage Vofs, that is tosay, at the low electric potential Vini.

In addition, at this time, the gate-source voltage Vgs of the drivetransistor Tdrv becomes Vofs−Vini. Here, because the threshold valuecorrection processing to be described later cannot be performed unlessVofs−Vini is larger than the threshold voltage Vth of the drivetransistor Tdrv, it is necessary to set a relationship satisfyingVofs−Vini >Vth.

In this manner, processing of performing initialization by fixing theelectric potential of the Gate to the reference voltage Vofs, and fixingthe electric potential of the Source to low electric potential Vini isprocessing of preparation (threshold value correction preparation)performed before the threshold value correction processing (Vthcorrection) to be described later is performed.

Subsequently, at a time t2, when the electric potential of the powersupply line DS switches from the low electric potential Vini to the highelectric potential Vccp, the threshold value correction processing (Vthcorrection) is started in a state in which the electric potential of theGate is maintained at the reference voltage Vofs. In other words, theelectric potential of the Source starts to rise toward an electricpotential obtained by subtracting the threshold voltage Vth of the drivetransistor Tdrv from the electric potential of the Gate.

When the threshold value correction processing proceeds, the gate-sourcevoltage Vgs of the drive transistor Tdrv eventually converges to thethreshold voltage Vth of the drive transistor Tdrv. The voltagecorresponding to the threshold voltage Vth is held in the holdcapacitance Cs.

Note that, in a period in which the threshold value correctionprocessing is performed (threshold value correction period), for causingcurrent to flow exclusively to the hold capacitance Cs side, and not toflow to the organic EL device OLED side, an electric potential Vcath isset to the power supply line so that the organic EL device OLED enters acut-off state.

Subsequently, at a time t3, by the electric potential of the scanningline WS shifting to the low electric potential side, the video signalwriting transistor Tsig enters the nonconductive state. At this time,the gate electrode of the drive transistor Tdrv enters a floating stateby being electrically separated from the signal line 16. Nevertheless,because the gate-source voltage Vgs is equal to the threshold voltageVth of the drive transistor Tdrv, the drive transistor Tdrv is in thecut-off state. Accordingly, the drive current Ids does not flow to thedrive transistor Tdrv.

Subsequently, at a time t4, the electric potential of the signal line 16switches from the reference voltage Vofs to the signal voltage Vsig ofthe video signal. Subsequently, at a time t5, by the electric potentialof the scanning line WS shifting to the high electric potential side,the video signal writing transistor Tsig enters the conductive state,samples the signal voltage Vsig of the video signal, and writes thevideo signal into the pixel 15.

By the writing of the signal voltage Vsig that is performed by the videosignal writing transistor Tsig, the electric potential of the Gatebecomes the signal voltage Vsig. Then, in driving the drive transistorTdrv using the signal voltage Vsig of the video signal, the thresholdvoltage Vth of the drive transistor Tdrv is balanced out by the voltagecorresponding to the threshold voltage Vth that is held in the holdcapacitance Cs.

At this time, the organic EL device OLED is in the cut-off state (highimpedance state). Accordingly, the drive current Ids flowing from thepower supply line DS to the drive transistor Tdrv in accordance with thesignal voltage Vsig of the video signal flows into the equivalentcapacitance of the organic EL device OLED and the auxiliary capacitanceCel. The charging of the equivalent capacitance of the organic EL deviceOLED and the auxiliary capacitance Cel is thereby started.

By the equivalent capacitance of the organic EL device OLED and theauxiliary capacitance Cel being charged, the electric potential of theSource rises as time goes on. At this time, a variation in the thresholdvoltage Vth of the drive transistor Tdrv among pixels has been alreadycancelled, and the drive current Ids of the drive transistor Tdrvbecomes current dependent on mobility μ of the drive transistor Tdrv.Note that the mobility μ of the drive transistor Tdrv is mobility of asemiconductor thin film forming a channel of the drive transistor Tdrv.

Here, it is supposed that a ratio of hold voltage (gate-source voltageof the drive transistor Tdrv) Vgs of the hold capacitance Cs withrespect to the signal voltage Vsig of the video signal, that is to say,a writing gain is 1 (ideal value). In this case, by the electricpotential of the Source rising up to an electric potential ofVofs−Vth+ΔV, the gate-source voltage Vgs of the drive transistor Tdrvbecomes Vsig−Vofs+Vth−ΔV.

In other words, a rise amount ΔV of the electric potential of the Sourceacts so as to be subtracted from the voltage (Vsig−Vofs+Vth) held in thehold capacitance Cs, that is to say, so as to discharge chargedelectrical charge of the hold capacitance Cs. In other words, the riseamount ΔV of the electric potential of the Source functions as anegative feedback to be applied to the hold capacitance Cs. Accordingly,the rise amount ΔV of the electric potential of the Source becomes afeedback amount of the negative feedback.

In this manner, by applying the negative feedback to the gate-sourcevoltage Vgs using a feedback amount ΔV corresponding to the drivecurrent Ids flowing in the drive transistor Tdrv, dependence on themobility μ of the drive current Ids of the drive transistor Tdrv can becancelled out. The processing is the mobility correction processing ofcorrecting a variation in the mobility μ of the drive transistor Tdrvamong pixels.

Subsequently, at a time t6, by the scanning line WS shifting to the lowelectric potential side, the video signal writing transistor Tsig entersthe nonconductive state. The gate electrode of the drive transistor Tdrvthereby enters the floating state because of being electricallyseparated from the signal line 16.

Here, when the gate electrode of the drive transistor Tdrv is in thefloating state, by the hold capacitance Cs being connected between thegate and the source of the drive transistor Tdrv, the electric potentialof the Gate also varies in conjunction with a variation in the electricpotential of the Source.

In this manner, an operation in which the gate electric potential of thedrive transistor Tdrv varies in conjunction with a variation in sourceelectric potential, that is to say, an operation in which the gateelectric potential and the source electric potential of the drivetransistor Tdrv rise while maintaining the gate-source voltage Vgs heldin the hold capacitance Cs is a so-called bootstrap operation.

By the gate electrode of the drive transistor Tdrv entering the floatingstate, and at the same time, the drive current Ids of the drivetransistor Tdrv starting to flow in the organic EL device OLED, an anodeelectric potential of the organic EL device OLED rises.

Then, when the anode electric potential of the organic EL device OLEDexceeds Vthel+Vcath, drive current starts to flow in the organic ELdevice OLED, and the organic EL device OLED starts to emit light. Inaddition, a rise in the anode electric potential of the organic ELdevice OLED is nothing less than a rise in a source electric potentialof the drive transistor Tdrv, that is to say, the electric potential ofthe Source. Then, when the electric potential of the Source rises, theelectric potential of the Gate also rises in conjunction therewith, bythe bootstrap operation of the hold capacitance Cs.

At this time, in a case where a bootstrap gain is supposed to be 1(ideal value), a rise amount of the electric potential of the Gatebecomes equal to a rise amount of the electric potential of the Source.Accordingly, during the light emitting period, the gate-source voltageVgs of the drive transistor Tdrv is maintained constant atVsig−Vofs+Vth−ΔV. Then, at a time t7, the electric potential of thesignal line 16 switches from the signal voltage Vsig of the video signalto the reference voltage Vofs.

In a series of circuit operations described above, respective processingoperations of the threshold value correction preparation, the thresholdvalue correction, the writing of the signal voltage Vsig (signalwriting), and the mobility correction are executed in one horizontalscanning period (1H). In addition, the respective processing operationsof the signal writing and the mobility correction are concurrentlyexecuted in a period of the times t5 to t6.

The operation example of the pixel 15 of the organic EL displayapparatus 1 according to the embodiment of the present disclosure hasbeen described above using FIG. 4 . Subsequently, an example of a crosssection of the pixel 15 of the organic EL display apparatus 1 accordingto the embodiment of the present disclosure will be described.

1.4. Cross-Sectional Example

As described above, in the pixel 15 of the organic EL display apparatus1 according to the embodiment of the present disclosure, the MOStransistor formed on the Si semiconductor substrate is used as the videosignal writing transistor Tsig, and the TFT is used as the drivetransistor Tdrv, and both transistors are separately used.

FIG. 5 is an explanatory diagram illustrating a configuration example ofcross sections of the video signal writing transistor Tsig and the drivetransistor Tdrv that are formed in the pixel 15 of the organic ELdisplay apparatus 1 according to the embodiment of the presentdisclosure.

The video signal writing transistor Tsig is formed in such a manner thatsource/drain regions 111 and 112 are formed in a Si substrate 101, and agate electrode 114 is formed on a gate insulator film 115 so as to besurrounded by a side wall 113.

On the other hand, the drive transistor Tdrv is formed in such a mannerthat source/drain regions 121 and 122 are formed on the upper side of anoxidized film 102 formed on the Si substrate 101, and a gate electrode125 is formed on a gate insulator film 124.

In this manner, by using the MOS transistor formed on the Si substrate101, as the video signal writing transistor Tsig, and using the TFT asthe drive transistor Tdrv, it becomes possible for the organic ELdisplay apparatus 1 according to the embodiment of the presentdisclosure to achieve higher quality of videos and to avoid a decline inuniformity.

FIG. 6 is an explanatory diagram illustrating another configurationexample of cross sections of the video signal writing transistor Tsigand the drive transistor Tdrv that are formed in the pixel 15 of theorganic EL display apparatus 1 according to the embodiment of thepresent disclosure. FIG. 6 illustrates cross-sectional examples of thevideo signal writing transistor Tsig and the drive transistor Tdrv thatare obtainable in a case where a Silicon on Insulator (SOI) substrate isused.

In the case of using the SOI substrate, the drive transistor Tdrv isformed by a buried oxidized film 103 being formed on the Si substrate101, the source/drain regions 121 and 122 being formed on the buriedoxidized film 103, and the gate electrode 125 being formed on the gateinsulator film 124. In addition, the video signal writing transistorTsig is formed by the source/drain regions 111 and 112 being formed onthe buried oxidized film 103, and the gate electrode 114 being formed onthe gate insulator film 115 so as to be surrounded by the side wall 113.

Note that, in the case of using the SOI substrate, it is only requiredthat the body region of the video signal writing transistor Tsig isgrounded for stabilizing an operation, and the body region of the drivetransistor Tdrv is intentionally brought into the floating state. Fordecreasing channel mobility of the drive transistor Tdrv, it is onlyrequired that an impure substance (e.g. argon (Ar), etc.) is selectivelyion-implanted only to a region in which the drive transistor Tdrv is tobe formed, making an SOI layer noncrystalline, and then, the drivetransistor Tdrv is formed as in FIG. 6 . In addition, for decreasingchannel mobility of the drive transistor Tdrv, a TFT to be used as thedrive transistor Tdrv may be formed after the SOI layer in the region inwhich the drive transistor Tdrv is to be formed is selectively removed.

In this manner, by using a MOS transistor formed on a Si substrate, asthe video signal writing transistor Tsig, and using a TFT as the drivetransistor Tdrv, the suppression of the substrate bias effect of thedrive transistor Tdrv can be realized in a smaller space as comparedwith a method of electrically separating the drive transistor Tdrv andthe drive transistor Tdrv using well separation.

FIG. 7 is an explanatory diagram illustrating a cross-sectional exampleof the pixel 15, and is an explanatory diagram illustrating an exampleof a case where the video signal writing transistor Tsig and the drivetransistor Tdrv are formed side by side in a horizontal direction.

As illustrated in FIG. 7 , the video signal writing transistor Tsig andthe drive transistor Tdrv may be formed side by side in the horizontaldirection, but for achieving higher definition of the pixel 15, thevideo signal writing transistor Tsig and the drive transistor Tdrv maybe formed in a stacked manner. In other words, the video signal writingtransistor Tsig may be formed on a Si substrate, and the drivetransistor Tdrv may be formed as a TFT in a wiring layer stacked on theupper side of the video signal writing transistor Tsig.

FIG. 8 is an explanatory diagram illustrating a cross-sectional exampleof the pixel 15 of the organic EL display apparatus 1 according to theembodiment of the present disclosure. In the pixel 15 illustrated inFIG. 8 , the video signal writing transistor Tsig is formed on the Sisubstrate 101, wiring interlayer films 131, 132, and 133 are formed onthe upper side of the video signal writing transistor Tsig, and the holdcapacitance Cs and the drive transistor Tdrv are formed in a region inwhich the wiring interlayer film 133 is formed. In addition, in thepixel 15 illustrated in FIG. 8 , wiring interlayer films 134, 135, and136 are formed on the upper side of the drive transistor Tdrv, and ananode electrode 151, an organic material layer 152, and a cathodeelectrode 153 are formed on the upper side of the wiring interlayer film135. Note that the organic EL device OLED is formed by the anodeelectrode 151, the organic material layer 152, and the cathode electrode153.

The video signal line (Vsig) 16 is connected to one source/drain regionof the video signal writing transistor Tsig via contact hole and contactvia 140, and the scanning line WS is connected to the gate electrode 114via the contact hole and contact via 140. In addition, the power supplyline DS is connected to one source/drain region 121 of the drivetransistor Tdrv via the contact hole and contact via 140, and oneelectrode 161 of the hold capacitance Cs is connected to the gateelectrode 125 via the contact hole and contact via 140. Anotherelectrode 162 of the hold capacitance Cs is connected to the anodeelectrode 151 of the organic EL device OLED.

By forming the video signal writing transistor Tsig on the Si substrate,and forming the drive transistor Tdrv as a TFT in the wiring layerstacked on the upper side of the video signal writing transistor Tsig,it becomes unnecessary to reduce a transistor size even if the drivecircuit is miniaturized for higher definition. Accordingly, by formingthe video signal writing transistor Tsig and the drive transistor Tdrvin a stacked manner as in FIG. 8 , the organic EL display apparatusaccording to the embodiment of the present disclosure has such an effectthat deterioration in uniformity that is caused by a variation intransistor characteristic can be avoided.

In addition, by forming the video signal writing transistor Tsig on theSi substrate, and forming the drive transistor Tdrv as a TFT in thewiring layer stacked on the upper side of the video signal writingtransistor Tsig, such an effect that it becomes unnecessary to shorten agate length of the drive transistor Tdrv is also obtained. This isbecause, if the gate length of the drive transistor Tdrv becomesshorter, current of the drive transistor Tdrv increases depending ondrain voltage.

FIG. 9 is an explanatory diagram illustrating an example of a voltagecurrent characteristic of the drive transistor Tdrv. In a graphillustrated in FIG. 9 , a broken line indicates an example of an idealvoltage current characteristic, and a solid line indicates an example ofan actual voltage current characteristic. Ideally, the drain current Idof the drive transistor Tdrv remains unchanged even if drain-sourcevoltage Vds of the drive transistor Tdrv declines to some degree.Nevertheless, when the gate length of the drive transistor Tdrv becomesshorter, actually, because the drain current Id also declines as thedrain-source voltage Vds of the drive transistor Tdrv declines,luminance deteriorates.

Nevertheless, by elongating the gate length of the drive transistorTdrv, the voltage current characteristic of the drive transistor Tdrvcan be brought closer to an ideal state. In other words, by elongatingthe gate length of the drive transistor Tdrv, the drain current Id doesnot decline due to the decline in the voltage Vds, and the deteriorationin luminance can be avoided. In other words, the drive transistor Tdrvcan be used in a state close to a constant current source.

In addition, when the video signal writing transistor Tsig and the drivetransistor Tdrv are formed side by side, in some cases, an adjacentdrive circuit can possibly cause a false operation due to parasiticcapacitance or parasitic leak at a PN junction formed inside thesubstrate, and information different from information originallyintended to be output can be possibly displayed. In contrast to this, asin FIG. 8 , by locating the video signal writing transistor Tsig and thedrive transistor Tdrv away from each other via the wiring interlayerfilms 131, 132, and 133 (e.g. via an oxidized film of 500 nm or more),such a false operation can be avoided.

FIG. 8 illustrates an example in which a Metal Insulator Metal (MIM)capacitor is used as the hold capacitance Cs, but a Metal InsulatorSemiconductor (MIS) capacitor may be used as the hold capacitance Cs.

FIG. 10 is an explanatory diagram illustrating another cross-sectionalexample of the pixel 15 of the organic EL display apparatus 1 accordingto the embodiment of the present disclosure. The pixel 15 illustrated inFIG. 10 is an example in which a MIS capacitor is used as the holdcapacitance Cs. The MIS capacitor can reduce a film thickness of adielectric film as compared with a case where a MIM capacitor formed ina wiring layer is used as the hold capacitance Cs. For example, the MIScapacitor can make the dielectric film into an oxidized film having afilm thickness of 10 nm or less. Thus, a gate oxidized film thickness ofthe video signal writing transistor Tsig and an insulator film thicknessof the hold capacitance Cs formed by the MIS capacitor can be madedifferent. Accordingly, by using the MIS capacitor as the holdcapacitance Cs, high capacitance can be ensured with a small area.

Note that, in a case where the video signal writing transistor Tsig andthe hold capacitance Cs are formed side by side as illustrated in FIG.10 , the same insulating film as that of the video signal writingtransistor Tsig may be used for the hold capacitance Cs, and for highercapacitance of the hold capacitance Cs, dielectric films of the videosignal writing transistor Tsig and the hold capacitance Cs may beindividually created separately.

2. Conclusion

As described above, according to an embodiment of the presentdisclosure, there is provided the organic EL display apparatus 1 thatuses transistors different in carrier mobility, as a drive transistorand a video signal writing transistor, such as a MOS transistor formedon a monocrystal Si substrate, as a video signal writing transistor, anda TFT as a drive transistor, for example.

By using transistors different in carrier mobility, as a drivetransistor and a video signal writing transistor, the organic EL displayapparatus 1 according to the embodiment of the present disclosure canmaintain signal quality at high quality, and in addition, can avoidimpairment in the uniformity of the screen that is caused by applicationof excessive mobility correction, without causing luminancedeterioration.

The organic EL display apparatus 1 according to the embodiment of thepresent disclosure can form a drive transistor and a video signalwriting transistor that are different in carrier mobility, in a stackedmanner via wiring interlayer films. By stacking the drive transistor andthe video signal writing transistor via the wiring interlayer films, thegate length of the drive transistor can be elongated, and the drivetransistor Tdrv can be used in a state close to a constant currentsource. In addition, by stacking the drive transistor and the videosignal writing transistor via the wiring interlayer films, couplingbetween the drive transistor and the video signal writing transistor canbe suppressed, and a false operation in which information different frominformation originally intended to be output is displayed can beavoided.

The organic EL display apparatus 1 according to the embodiment of thepresent disclosure can be mounted on various devices. For example, theorganic EL display apparatus 1 according to the embodiment of thepresent disclosure can be mounted on various devices such as atelevision receiver, a personal computer, a mobile phone, asophisticated mobile phone (smartphone), a tablet-type mobile terminal,a portable music player, a game machine, a digital still camera, adigital video camera, and other wearable computers such as awristwatch-type computer, a head-mounted computer, and a pendant-typecomputer.

The preferred embodiment(s) of the present disclosure has/have beendescribed above with reference to the accompanying drawings, whilst thepresent disclosure is not limited to the above examples. A personskilled in the art may find various alterations and modifications withinthe scope of the appended claims, and it should be understood that theywill naturally come under the technical scope of the present disclosure.

For example, in the above embodiment, an organic EL device is used as alight emitting device, but this technology is not limited to thisexample. For example, also in a display apparatus that uses aself-light-emitting type light emitting unit such as an inorganicelectroluminescence light emitting unit, an LED light emitting unit, anda semiconductor laser light emitting unit, transistors different incarrier mobility may be used as a drive transistor and a video signalwriting transistor, similar to the above embodiment.

Further, the effects described in this specification are merelyillustrative or exemplified effects, and are not limitative. That is,with or in the place of the above effects, the technology according tothe present disclosure may achieve other effects that are clear to thoseskilled in the art from the description of this specification.

Additionally, the present technology may also be configured as below.

(1)

A display apparatus including:

-   -   a plurality of light emitting devices each including a light        emitting unit and a drive circuit for driving the light emitting        unit,    -   in which the drive circuit includes    -   a drive transistor configured to control the light emitting        unit,    -   a video signal writing transistor configured to control writing        of a video signal, and    -   a capacitative element,    -   in the drive transistor, one source/drain region is connected to        a current supply line, another source/drain region is connected        to the light emitting unit and a first node of the capacitative        element, and a gate electrode is connected to a second node of        the capacitative element,    -   in the video signal writing transistor, one source/drain region        is connected to a data line, another source/drain region is        connected to the gate electrode of the drive transistor and the        second node of the capacitative element, and a gate electrode is        connected to a scanning line, and    -   the drive transistor and the video signal writing transistor are        different in carrier mobility.        (2)

The display apparatus according to (1), in which carrier mobility of thedrive transistor is lower than carrier mobility of the video signalwriting transistor.

(3)

The display apparatus according to (1), in which the video signalwriting transistor is formed on a silicon semiconductor substrate, and athin film transistor is used as the drive transistor.

(4)

The display apparatus according to (2), in which the drive transistor isan n-channel type MOS transistor.

(5)

The display apparatus according to (2) or (3), in which the drivetransistor is formed in a wiring layer.

(6)

The display apparatus according to (5), in which the drive transistorand the video signal writing transistor are formed at positions at leastpartially overlapping in a horizontal direction.

(7)

The display apparatus according to any of (1) to (6), in which, in thecapacitative element, a source/drain region of the drive transistor isused as a first node, and a source/drain region of the video signalwriting transistor is used as a second node.

(8)

The display apparatus according to (7), in which the capacitativeelement is a Metal Insulator Semiconductor (MIS) capacitor.

(9)

The display apparatus according to (8), in which a gate oxidized filmthickness of the video signal writing transistor and an insulator filmthickness of the MIS capacitor are different.

(10)

An electronic device including:

-   -   the display apparatus according to any of (1) to (9).

REFERENCE SIGNS LIST

-   1 organic EL display apparatus-   11 pixel array portion-   12 light scanner-   13 drive scanner-   14 horizontal selector-   15 pixel-   16 signal line-   32 power supply line-   101 Si substrate-   102 oxidized film-   103 buried oxidized film-   111 source/drain region-   112 source/drain region-   113 side wall-   114 gate electrode-   115 gate insulator film-   121 source/drain region-   122 source/drain region-   124 gate insulator film-   125 gate electrode-   131 wiring interlayer film-   132 wiring interlayer film-   133 wiring interlayer film-   134 wiring interlayer film-   135 wiring interlayer film-   136 wiring interlayer film-   140 contact hole and contact via-   151 anode electrode-   152 organic material layer-   153 cathode electrode-   161 electrode-   162 electrode-   Cs hold capacitance-   Cel auxiliary capacitance-   DS power supply line-   Tdrv drive transistor-   Tsig video signal writing transistor-   WS scanning line

1. (canceled)
 2. A display apparatus comprising: a substrate; and aplurality of light emitting devices formed on the substrate,respectively including a light emitting element and a drive circuit fordriving the light emitting element, wherein the drive circuit includes afirst transistor configured to control the light emitting element, asecond transistor configured to write a video signal, and a capacitativeelement, and wherein a first terminal of the first transistor isconnected to an anode electrode of the light emitting element, a firstterminal of the second transistor is connected to a signal line, asecond terminal of the second transistor is connected to a firstelectrode of the capacitative element, a first semiconductor layer ofthe first transistor is located between a top surface of the substrateand the anode electrode of the light emitting element in across-sectional view, and a material of the first semiconductor layer ofthe first transistor and a material of a second semiconductor layer ofthe second transistor are different.
 3. The display apparatus accordingto claim 2, wherein the first transistor is a driving transistor and thesecond transistor is video signal writing transistor.
 4. The displayapparatus according to claim 2, wherein the first transistor is a MOStransistor.
 5. The display apparatus according to claim 2, wherein thecapacitative element is Metal Insulator Metal (MIM) capacitor.
 6. Thedisplay apparatus according to claim 2, wherein the substrate is a Sisubstrate.
 7. The display apparatus according to claim 2, wherein thefirst semiconductor layer is an oxide film.